What is over packing and under packing in injection molding

Over-Packing" and "Under-Packing":

1. Over-packing: When some flow paths are still filling, some flow paths have begun to compress the additional plastic.

2. Under-packing: It means that after the pressure holding action is completed, the melt has not been filled or compacted.

Both over-packing and under-packing are manifestations of abnormal packing pressure, which will produce defects in the workpiece.

In plastic injection molding, the melt injected into the cavity will shrink due to cooling, so the screw should continue to move forward slowly, so that the melt in the barrel continues to be injected into the cavity to supplement the need for product shrinkage, the above process is called pressure holding. Choosing the appropriate holding time and holding pressure can effectively prevent the product from shrinking, and the product production is relatively stable. The appropriate holding method can adjust the size of the product without weld lines, dents, flashes and warping, and achieve ideal product quality control.

This is an abnormal phenomenon other than normal pressure holding, and it is really difficult to say that the specific definition is clear, which is also the word summarized by the experience of injection molding machine.

The role of pressure holding in the injection molding machine is:

1. Pressure holding can control the deformation and size of the product.

2. When the product is melted, cooled, solidified and shrinked, maintain a pressure, continue to inject melt to fill the shrinkage space, reduce or avoid the occurrence of dent rolling.

3. Due to the reduction of the plastic temperature and the internal stress inside, the plastic in the mold cavity will reflux, if there is no pressure holding to eliminate the pressure and remove the pressure, the product will shrink or not satiety.

The function of holding pressure is to maintain a pressure when it melts and cools and cures and shrinks, and continues to inject melt to fill the shrinkage space, reducing or avoiding the occurrence of dents.

The set pressure of the holding section should not exceed the set pressure of the extrusion section, otherwise the burr may be generated in the holding section. The holding pressure of multiple stages is reduced in each stage, and the ideal decline is a linear gradual decrease, non-hierarchical decline, to meet the actual needs of gradual contraction.

Due to the slow contraction, the forward speed of the screw is also slow, e.g. 2% speed is sufficient. The energy saving of the injection molding machine is mainly to reduce the flow rate of the pump to such as 3% when maintaining pressure, which is 97% compared with the quantitative pump where the flow rate is always 100%. The longer the dwell time (with very large wall thicknesses), the more power consumption is saved.

It can be seen that only the pressure needs to be controlled but not the flow rate when holding pressure, because the shrinkage rate is not controlled by the injection molding machine, which is just the opposite of the pre-injection stage.

The holding pressure is to compensate for the sealing of the injection channel at the end of injection and the high cavity due to volume shrinkage, so the holding pressure must be higher than the internal residual pressure. The appropriate holding time is the time to maintain until the gate solidifies, and the size of the holding pressure and the holding time should be properly matched.

Injection pressure holding is "the injection of plastic into other items to maintain its specific pressure".

Injection molding: Injection molding is a method of producing moldings for industrial products. Beijing Fuhua Plastic Industry **** products usually use rubber injection molding and plastic injection molding.

Injection molding can also be divided into injection molding and compression molding. and die casting. Injection molding machine (referred to as injection machine or injection molding machine) is the main molding equipment for making thermoplastics or thermosets into plastic products of various shapes using plastic molding molds, and injection molding is achieved through injection molding machines and molds.

Injection molding products are widely used in: mobile phones, laptops, a variety of plastic shells, communications, micro-motors, computers, electrical appliances, electronics, toys, clocks, lighting, locomotives and other industries.

Holding pressure is the shrinkage of the molded plastic due to the decrease in temperature caused by the filling of the mold with a very slow injection speed. The purpose is to reduce product deformation.

Personal understanding.

Injection molding machine du

During the working process of the pressure holding injection molding machine.

Closing zho -- A DAO mold divided into two halves. Control the hydraulic cylinder to close the mold and stabilize the pressure and maintain the pressure -- after the mold is closed, the hydraulic pressure still maintains a certain pressure so that the plastic can be injected into the mold.

After the decompression 、-- plastic is injected into the mold, the pressure on the mold is released by controlling the hydraulic pressure.

The brake opening 、-- control the hydraulic cylinder to separate the molds. so that the workpiece can be removed.

Mold clamping, injection, pressure holding, material storage, cooling, mold opening.

1. The pressure holding is that after the mold is filled with glue or the injection time is completed, the injection cylinder still maintains a certain pressure and the screw stays still, (not to the mold) to consolidate the plastic parts without shrinkage and improve the quality of the plastic parts.

2. Inspection of injection molding machine:

Check before use:

1.Check the amount of oil in the tank. Determined within the oil quantity standard.

2.Check the room heat and oil temperature. The oil should be preheated at low temperature indoors. For high indoor temperature, heat dissipation should be done.

3.Check the pressure gauge to see if the swing is serious, whether it can return to zero and mileage status.

4.Check the temperature control system.

Check in use:

1.When activating, the relief valve is adjusted to the lowest pressure.

2.Check and adjust the regulating pressure of the relief valve, whether it rises and falls continuously and evenly, and then adjust to the set pressure after everything is normal.

3.The oil temperature of 20 degrees to 50 degrees Celsius is normal, and the temperature of the pump casing is 10 degrees Celsius to 30 degrees Celsius higher than the room temperature.

4.Oil spill inspection.

5.Noise and vibration checks.

6.Pressure gauge check.

7.Check the working condition of electrical components and the reliability of safety devices.

8.Whether the fastening nut screws of each column cylinder element are loose.

Post-shutdown inspections:

1.Check the oil level of the fuel tank.

2.Check the hydraulic components.

3.The position of each valve handle should be restored to the position of "pressure relief", "stop" and "retreat".

4.Check whether the control switch button and electrical components are loose and sensitive.

5.The moving parts of the movable connection between the column and the oil-impregnated bearing are lubricated with oil.

6.Turn off the power and do a good job of safety.

The holding pressure is to compensate for the sealing of the injection channel at the end of injection and the shrinkage due to volume shrinkage, so the holding pressure must be higher than the residual pressure inside. The appropriate holding time is to maintain the time until the gate solidifies, and at the same time, the size of the holding pressure and the holding time are properly matched

To give you a statement that you can understand: pressure holding is that after the mold is filled with glue or after the injection time is completed, the injection cylinder still maintains a certain pressure and the screw stays still, (not to shoot glue into the mold) to consolidate the plastic parts without shrinkage and improve the quality of the plastic parts.

In the injection molding process, the melt shrinks due to cooling, but because the screw continues to move forward slowly, the melt in the barrel continues to be injected into the cavity to supplement the need for product shrinkage, which is called pressure holding. To put it bluntly, it is to prevent the shrinkage of the product, and the production of the product is relatively stable if the pressure is maintained. Packing can also adjust the size of the product without weld lines, dents, flashes and warping.

In fact, both pressure holding and injection mean the same thing, that is, push the screw forward with force, but in the injection process, the injection speed is set and the maximum injection pressure is the upper limit of the push, and in the pressure holding process, the injection pressure is set and the maximum pressure holding speed is the upper limit of the push.